1. Field of the Invention
The invention relates generally to audio amplification systems, and more particularly to systems and methods for detecting a variety of potential failure conditions in a digital amplification system and providing a programmable response to the detected failure conditions.
2. Related Art
Pulse Width Modulation (PWM) or Class D signal amplification technology has existed for a number of years. PWM technology has become more popular with the proliferation of Switched Mode Power Supplies (SMPS). Since this technology emerged, there has been an increased interest in applying PWM techniques in signal amplification applications as a result of the significant efficiency improvement that can be realized through the use of Class D power output topology instead of the legacy (linear Class AB) power output topology.
Early attempts to develop signal amplification applications utilized the same approach to amplification that was being used in the early SMPS. More particularly, these attempts utilized analog modulation schemes that resulted in very low performance applications. These applications were very complex and costly to implement. Consequently, these solutions were not widely accepted. Prior art analog implementations of Class D technology have therefore been unable to displace legacy Class AB amplifiers in mainstream amplifier applications.
Recently, digital PWM modulation schemes have surfaced. These schemes use Sigma-Delta modulation techniques to generate the PWM signals used in the newer digital Class D implementations. These digital PWM schemes, however, did little to offset the major barriers to integration of PWM modulators into the total amplifier solution. Class D technology has therefore continued to be unable to displace legacy Class AB amplifiers in mainstream applications.
One of the problems is that prior art means for protecting the PWM amplifier circuitry are not very efficient or effective. Because PWM amplifiers handle high currents and voltages, there is a danger that the amplifiers may fail in a catastrophic manner. For example, the amplifiers may be driven until they overheat and burn up their circuitry.
Existing protection schemes make use of traditional analog-based circuits. These circuits have a number of shortcomings. For instance, prior art protection circuits conventionally have to be characterized and adjusted in a laboratory environment. Once the design of a protection circuit is finalized, it is not possible to adjust the circuit in a particular amplifier. As a result of manufacturing tolerances, the actual operation of the circuit can vary significantly from one amplifier to another. The RC circuits that provide the time constant mechanisms in the design are particularly vulnerable to manufacturing tolerances. The circuit may therefore operate as intended in one device, while initiating a response to a failure condition either too quickly or too slowly in another device.
Another of the shortcomings of conventional protection circuits is that the response to a particular failure condition is fixed. Typically, the response will simply be to shut down the amplifier upon detecting the failure condition. While this response may be appropriate for a condition such as excessive current in the amplifier (which could destroy the amplifier's circuitry), it may not be appropriate for a condition such as a temperature that is slightly elevated, but that would not cause immediate damage to the system.
Still another of the shortcomings of conventional protection schemes is that they typically require a separate circuit to handle each of the potential failure conditions. The need for separate circuitry increases the complexity of the overall system design and consequently increases the likelihood of related problems, such as component failures, power consumption, heat build up, and the like.
It would be desirable to provide a protection schemes for a digital PWM amplification system that did not suffer from these shortcomings.